Nice "how to" indeed!
Dspam seems to be a good alternative for spamassassin,
but it requires "training" which means that you have to teach what is spam or not. Training is necessary to avoid mistakes. (sometimes normal mail is recognised as spam and visa versa). With training spamd can be more effective than spamassassin, but i do not know if training is very userfriendly for clients.

An advantage of dspam is that it is lightweight as it is written in C and not in Perl. This means when your MTA is attacked by a lot of spam, the mailprocess is not slowing down so much.

I will give dspam a try in the (near) future, but not right now, because i am very satisfied with spamassassin!